Newly Single Jon Hamm Enjoys a Guys' Night Out in Los Angeles -- See the Pics

It appears Jon Hamm is leaning on his guy friends for support, in the wake of his surprising split with Jennifer Westfeldt after 18 years together.

The 44-year-old former Mad Men star was spotted enjoying dinner with two pals at Little Dom's restaurant in Los Angeles on Thursday night, going casual in a baseball hat, a black polo shirt and cream pants. Hamm was spotted giving his friend a hug at one point, smiling and appearing to be in good spirits during the meet-up. The handsome actor's bro night marks the first time he's been seen out and about since he and Westfeldt announced their split on Labor Day.

A source tells ET that Hamm stuck to water for the night. In March, he completed treatment in a rehab facility, where he sought help in battling an alcohol addiction.

Though Hamm and Westfeldt announced their split just this Monday, a source previously ET that the two have actually been broken up for a few months now. According to the source, Hamm's "party-heavy lifestyle" got to be too much for the 45-year-old Kissing Jessica Stein writer/actress.

"Jon and Jennifer really fought hard to make their relationship work, Jennifer more so than Jon," the source says. "They were together for many years, but in the end, it was too much work. It's no secret that Jon likes to go out and leads a very party-heavy lifestyle. And Jennifer was just tired of that."

"She wanted him to grow up … and he never wanted to," the source adds. "She was tired of being his mother."

The former couple has been dating since 1997, after meeting each other at a party. They announced their split in a joint statement to ET. "With great sadness, we have decided to separate, after 18 years of love and shared history," the statement reads. "We will continue to be supportive of each other in every way possible moving forward."